1. Field of the Invention
The present invention relates to a gear-shift mechanism for a manual transmission in automotive vehicles, and more particularly to a power-assisted gear-shift mechanism capable of providing a hydraulic power assist to the operator's effort applied to a manual shift lever of the transmission in shifting operation thereof.
2. Discussion of the Background
In conventional manual transmissions, selecting operation of the manual shift lever is effected by a small effort. It is, however, required to apply a large effort to the manual shift lever in shifting operation thereof particularly in an automotive vehicle equipped with a prime mover of large torque and a large size clutch assembly. In Japanese Utility Model Early Publication No. 48-38276, there has been proposed a power-assisted gear-shift mechanism which is provided with a pneumatic power cylinder assembly for providing a pneumatic power assist to the operator's effort applied to the manual shift lever in shifting operation thereof. The power cylinder assembly includes a cylinder casing, a piston rod axially slidably disposed within the cylinder casing in an air-tight manner to subdivide the interior of the casing into two pressure chambers, and a valve mechanism for selectively supplying the air under pressure to the pressure chambers through the piston rod. However, the valve mechanism is composed of a large number of component parts and complicated in construction, resulting in an increase of manufacturing cost.